In recent years, an optical filter in which light in a visible wavelength region (450 nm to 600 nm) is fully transmitted but light in a near-infrared wavelength region (700 nm to 1100 nm) is shielded has been used for various uses.
For example, in imaging devices such as a digital still camera, a digital video using a solid-state image sensor (CCD, CMOS and so on) and a display device such as an automatic exposure meter using a light-receiving element, the optical filter as stated above is disposed between an imaging lens and the solid-state image sensor or the light-receiving element so as to make sensitivity of the solid-state image sensor or the light-receiving element approximate to visibility of a human being. Besides, in a PDP (plasma display panel), the optical filter is disposed at a front surface (visible side) to prevent a malfunction of a remote control unit for a home electric appliance activated by the near infrared.
Among the above, a glass filter in which CuO and so on is added to a fluorophosphate-based glass and a phosphate-based glass so as to selectively absorb the light in the near infrared wavelength region is known as the optical filter for the imaging device, but a light-absorption type glass filter is expensive and it is difficult to reduce a thickness thereof, so there has been a problem that it is impossible to enough correspond to requirements for downsizing and reduction in thickness of the imaging device in recent years.
Accordingly, a reflection-type interference filter in which, for example, a silicon oxide (SiO2) layer and a titanium oxide (TiO2) layer are alternately stacked on a substrate to reflect and shield the light in the near infrared wavelength region by interference of light, a film in which dye absorbing the light in the near infrared wavelength region is contained in a transparent resin, and so on are developed to solve the above-stated problems. Besides, an optical filter in which the above are combined such that a resin layer containing the dye absorbing the near infrared and a layer reflecting the near infrared are stacked is also developed.
Among the above, a technology in which a polyester resin and a polycarbonate resin having a fluorene skeleton whose refractive index is high and heat resistance is excellent are used as the transparent resin in a film containing the dye absorbing the light in the near infrared wavelength region in the transparent resin has been developed. Besides, a technology of an anti-reflection composite function film in which an acrylic resin having the fluorene skeleton is used as a high refractive index layer of an anti-reflection film in which the high refractive index layers and low refractive index film layers are alternately stacked in consideration of an abrasion resistance, a chemical resistance, and so on in addition to the above-stated characteristics and further, a function of the optical filter is added to the high refractive index layer by making it contain a near infrared absorbent has been developed.
However, when the optical filter is enabled by forming the resin layer in which the near infrared absorbent is contained in the transparent resin having the fluorene skeleton on a glass substrate, there is a case when a problem occurs in adhesiveness, particularly in adhesiveness when it is exposed under a high-temperature and high-humidity environment for a long time, and it cannot necessarily be said that it has enough reliability. Besides, when the adhesivenesses between the resin layer and the glass substrate and between the resin layer and the anti-reflection film are insufficient, there is a problem in manufacturing to incur deterioration in yield when a base material obtained in a large size is cut by dicing to process into a production size.